The present invention relates to pipe organs, and more particularly to electrically augmented pipe organs and to means for keeping the pitch of the electronically produced musical tones in tune with the pitch of the tones produced by the organ pipes.
Since the early part of the twentieth century there has been much development in the field of electronic organs, which, for the most part, attempt to imitate the sounds of the pipe organ in which musical tones are produced by wind blown pipes. Much of the charm and character of the sounds from wind blown pipes is the result of the spacial distribution of the pipes, and the sounds they produce, as well as of the very complex nature of the tones themselves. These tones involve dissonant partials at the moment of speech, various types of modulation effects, and many other characteristics yet to be fully understood.
Although the sounds produced by pipe organs are highly desirable, such organs are bulky and expensive, and the larger pipes, which produce the lower pitched tones, require a great deal of wind. Accordingly, organs which utilize the large, bulky lower tones require large air blowers that are often noisy and and must frequently be placed in an out-of-the-way location and connected to the organ wind chests by large wind conductors, thus further increasing the cost and space required. Because of this, attempts have been made to augment pipe organs with electronic tone generation for some of the voices that can be satisfactorily produced by electronic means. Since, in general, the pipes increase in bulk geometrically with descending pitch, it is attractive to produce the tones of the lowest octaves electronically, since in this way much cost can be eliminated and a great deal of space can be saved. Furthermore, since tones in the lowest octaves are normally played monophonically (one note at a time), many of the limitations and compromises that would be involved in using electronic tone generation in the upper and middle octaves are avoided. This is especially true of the number of amplification channels needed to approach the full spacial effects that occur naturally with organ pipes where each and every note speaks from a different point in space.
A problem that must be overcome in a hybrid instrument, where some tones are produced by pipes and some by electronic tone generators, is that of keeping the pitch of the two tone generating systems in tune with one another. In general, electronic tone producers can be made to be quite stable and relatively unaffected by changes in temperature, humidity and atmospheric pressure. Organ pipes, on the contrary, are very much affected by these factors, moving in pitch almost two "cents" (one cent equals one-one hundreth of a semitone) for each degree Fahrenheit of temperature change, and it has been recognized for a long time that in hybrid organs it is necessary to provide means for overcoming this problem. Since there is no known practical way of simultaneously adjusting the tuning of many organ pipes in such a manner that their pitch will "track", it has been easier to vary the pitch of all of the electronically generated notes to bring them into consonance with the pipes at whatever temperature obtains. In my prior U.S. Pat. No. 2,818,759 issued Jan. 7, 1959, there is disclosed an electro-mechanical system designed to move individual pieces of a ferro-magnetic material in the field of each of a large number of individual tone oscillators that generated the electronic tones for a hybrid organ. The system was employed successfully, but was costly and difficult to construct and adjust and had a limited tuning range.
Another system that has been used in commercial hybrid organs involves the insertion of a voltage (or current) into an ordinary oscillator circuit for causing it to detune as the voltage (or current) is varied. These systems are very marginal in performance because each of the many oscillators involved moves to a greater or lesser degree than its neighbors, and thus they do not "track" uniformly. Furthermore, when it is attempted to tune oscillators very far from their nominal frequencies, other problems are usually encountered. For example, the oscillator may not start properly, or its tone or amplitude characteristics may change along with the pitch. In addition such oscillator systems are expensive to construct and adjust.